Method for manufacturing lead grid plates for batteries

ABSTRACT

A method for manufacturing a lead grid plate for batteries comprising the first process of preparing a rolled lead alloy plate measuring 0.5 to 1 mm in thickness; the second process of press punching the rolled lead alloy plate by means of a metal mold to obtain a lead grid plate, the width of the grid forming members of the plate measuring about the same as the thickness of the plate; and the third process of hardening said lead grid plate through a heat treatment with or without a prior shape correcting process carried out before the third process.

BRIEF SUMMARY OF THE INVENTION

This invention relates to a method for manufacturing lead grid platesusable for batteries and more particularly to a method for manufacturingsuch plates from rolled lead alloy plates through a press punchingprocess. In this method, the hardening of the lead alloy is accomplishedeither by preparing the rolled lead alloy plate through a hot rollingprocess or by carrying out a heat treatment before or after the presspunching process to increase the hardness of the lead grid plate for thepurpose of attaining an increased strength to facilitate the batteryassembling work, and at the same time, for making it possible to reducethe thickness of the lead grid plate, so that the weight of the batterycan be eventually reduced and its output can be increased. Furthermore,a continuous arrangement of the rolling, press punching and heattreatment processes also permits the continuous and efficient massproduction of such lead grid plates with high dimensional precision at alow cost.

BACKGROUND OF THE INVENTION

The conventional lead grid plates for battery are generally manufacturedby means of metal molds. The thickness of such cast grid plates is morethan 1.2 mm. Moreover the thickness of the transverse and verticalmembers inside the grid plate frame is more than 0.8 mm. It isimpossible to make them thinner, because any attempt to make themthinner results in a product partly lacking their grid constituentmembers.

In other words, in the casting process, it is impossible to ensure thatthe molten lead alloy reaches every part of the metal mold even when thetemperature of the mold is high. This results in the production ofunusable lead grid plates.

Yet, requirement for lead grid plates that are thinner than 1.2 mmrecently arised to make it possible to have more electrodes in onecontainer for the purpose of increasing the capacity of battery and alsoreducing their weight.

In addition to above-stated shortcoming, the casting process is notsuitable for continuous mass production in terms of cost and efficiency.It is another shortcoming of the casting process that the dimensionalprecision of the cast product is inferior and this presents a problem inthe automation of battery assembling processes.

In order to eliminate such shortcomings of the casting process, it isconceivable to manufacture lead grid plate through a press punchingprocess. However, although the press punching process permits making thewidth of the grid forming member about 1 mm when the plate thickness ismore than 1.2 mm, it is extremely difficult to make the width less than1 mm when the plate thickness is less than 1 mm. However, with the widthof the grid forming members wider than 1 mm, the amount of the activematerial that can be retained by the lead grid decreases. Then, with theretaining amount decreased, there is no sense in exerting the effort tomake the lead grid plate thinner.

Generally, is punching a metal plate of iron, aluminum, etc. into a gridshape by means of a press, it is impossible to make the width of thegrid forming members about the same as the thickness of the plate.Besides the lead alloy which is employed in manufacturing the lead gridplates for batteries is softer than iron, aluminum and other metals.This makes the press punching more difficult. The deformation andbreakage of the structural members of the grid tend to take place in thepunching process. It is thus difficult to obtain usable lead gridplates. This tendency is more stronger with a thin plate measuring lessthan 1 mm thickness and with narrow grid forming members measuring lessthan 1 mm width.

This invention solves these problems. In accordance with the inventedmethod, the thickness of the lead grid plate can be decreased to about0.6 mm and the width of the grid forming members also can be reduced toabout the same as the thickness. This is impossible by the conventionalcasting method. Besides, the invented method makes possible continuousproduction processes including preparation of lead grid plates fromstrips of a lead alloy obtained by a continuous casting process, fillingthe grid windows with an active material paste and obtaining dried,filled plates.

DETAILED DESCRIPTION OF THE INVENTION

The first object of this invention is to provide a thin lead grid plateby carrying out a heat treatment process for hardening the lead alloy ata suitable stage in the production comprising the preparation of arolled lead alloy plate, press punching and preparation of the lead gridplate so that the strength of the product can be increased by suchhardening. Such hardening heat treatment serves to eliminate thedifficulty of work caused by the deformation that would otherwise takesplace when an active material is applied to the lead grid plate.

Generally, in processing lead alloy, an ingot of the lead alloy softenswhen it is subjected to a cold rolling process and the hardness of theingot which is about 25 by Vickers hardness normally comes to decreaseto 7 or thereabout. This presents a very soft state, which makes theassembling work on battery hardly possible and this is the reason forcarrying out the hardening heat treatment.

With such treatment carried out in accordance with the invented method,the conventionally employed materials containing 4.2% Sb and even suchmaterials that contain 2% Sb can be made into grid plates of sufficienthardness.

The second object of this invention is to provide lead grid plates ofimproved hardness and accordingly of improved mechanical properties,which are attained by first subjecting a lead alloy plate softened bycold rolling to a press punching process to obtain a lead grid plate andthen by carrying out a heat treatment.

This object is attained through the combination and sequence comprisingthe first process for preparing a rolled lead alloy plate, the secondprocess for press punching the lead alloy plate by means of a metal moldto make it into a lead grid plate with the width of the grid formingmembers measuring about the same as the thickness of the plate and thethird process for hardening the lead grid plate by heat treatment afteror without shaping.

For this method, a base plate of the same thickness as the desiredthickness of the lead grid, say 0.5 to 1 mm, is obtained from an ingotthrough rolling. A lead-antimony alloy is generally employed for themanufacture of batteries. The hardness of the alloy in the state of aningot prepared by casting decreases as the degree of rolling increases.

Accordingly, the lead alloy base plate is softened by rolling in thefirst process. This facilitates punching with a press in the secondprocess, wherein a desired form of the lead grid plate is obtained bycarrying out press punching with a metal mold.

The punching process is accomplished using a punching mold whichcomprises a male mold and a female mold. The male mold has protrusionsin positions corresponding to the voids of the lead grid. In the femalemold, only the parts corresponding to the grid members serves for thepurpose of punching. For a narrow width of the grid forming members inthe range of 0.5 to 1 mm as in the case of this invention, the strengthof the female mold tends to be insufficient. When the lead grid baseplate to be press-punched is hard, such hardness requires a greaterpunching force, which tends to cause the deformation of the female moldor the breakage of the parts corresponding to the grid forming membersof the grid plate.

However, since the lead grid base plate has been softened by the rollingin the first process, the use of a small punching force suffices. Thisin turn also ensures a good grid shape of the lead grid plate besidesreducing the possibility of deforming the metal mold for a longerservice life and easier maintenance of the mold.

Meanwhile, the lead grid plate obtained through the second process istoo soft and does not have sufficient strength. The third process istherefore carried out to increase the hardness of the base plate whichhas been softened by the rolling process for the purpose of ensuringgood mechanical property of the product.

It is the third object of this invention to provide a simplifiedpunching process for obtaining a lead grid plate, wherein a rolled lendalloy plate which is hardened by heat treatment carried out duringand/or following the rolling process is subjected to a press punchingprocess in such a manner as not only to ensure ready separation of thepunched lead grid plate from the bottom of the mold but also to permitobtaining a punched plate without any additional process.

This object is attained by the combination and sequence of the firstprocess of preparing a rolled lead alloy plate, the second process ofhardening by heat treatment which is carried out either during orfollowing the first process and the third process for press punching thehardened, rolled lead alloy plate with a metal mold to obtain a leadgrid plate which has grid forming members of width measuring about thesame as the thickness of the plate.

Since the press punching process is carried out on a hardened rolledplate with a metal mold, a lead grid plate wherein the width of the gridmembers measures about the same as the plate thickness can be obtainedwith a high degree of precision. In addition to such an advantage, thelead grid plate is free from deformation by punching so that a productof good flatness can be obtained requiring no additional process forfinish shaping.

Furthermore, since the lead grid plate is obtained by punching ahardened rolled plate, the product thus obtained retains the samehardness of the hardened rolled plate. This ensures good mechanicalproperties of the product.

It is the fourth object of this invention to provide a process forfacilitating the preparation of lead grid plates wherein press punchingby means of metal molds is carried out stepwise to facilitate thepreparation of lead grid plates.

With the multistep punching process employed, the number of thecritically narrow parts of the punching metal mold measuring, say, 0.5 -1.0 mm can be minimized so that its service life can be increased.

As mentioned in the foregoing, the hardness of the rolled lead alloyplate decreases as the degree of rolling increases. While such decreasein the hardness permits the use of a smaller punching force for presspunching the rolled plate, the extreme thinness of the plate tends toresults in the deformation of the lead grid plate, particularly in thedeformation of the grid members. The desired form of the plate issometimes hardly retainable.

To solve this problem, the shape of the lead grid plate is correctedafter press punching and before the hardening process is carried out byheat treatment. Though this enables the deformation due to presspunching to be corrected to a certain degree, such deformation is oftenbeyond correction and the desired lead grid plate is hardly obtainable.

Such a problem can be solved by the above stated multistep punchingprocess, which is carried out by punching the rolled lead alloy platestepwise, instead of punching in one step, in a suitable way such aspunching every alternate file or row or in a zigzag manner whileavoiding the deformation of the grid plate. This method minimizes thedeformation of the lead grid plate. And, even if there is left somedeformation, such deformation can be eliminated by a flattening processcarried out before the hardening heat treatment, so that a lead gridplate of high quality can be otained.

For the above stated multistep press punching process, a suitable methodof uniformely carrying out the process without causing local deformationof the lead grid plate is selected. The preferred modes of carrying outthe process include, for example, the above-stated alternate punchingand zigzag punching which permit easy correction of deformation in thenext process as necessary.

The press punching in each step may be accompanied by correction ofdeformation in such a way as to alternately performing the punching andthe shape correction.

In the multistep press punching process, the shape of the lead gridplate is corrected before the base plate which has been softened byrolling is hardened by a heat treatment process for improved mechanicalproperties. However, such hardening heat treatment may be carried outbefore the multistep press punching process.

It is the fifth object of this invention to provide a process forattaining an improved active material retainability of the lead gridplate wherein the deformation of the lead grid plate resulting from theabove-stated multistep press punching process is retained and fixed asit is.

Since the hardness of the rolled lead alloy plate decreases as thedegree of rolling applied to it increases, the press punching of theplate with a metal mold can be accomplished with a small punching forceas already mentioned in the foregoing. This, on the other hand, requiresan additional work for correcting the deformation of the lead grid plateand particularly that of its grid forming members as such deformationtends to take place due to the extreme thinness of the rolled plate,such as 0.5 to 1 mm.

In attaining the fifth object of this invention, such deformation isutilized with advantage, and the active material retaining ability ofthe lead grid plate is enhanced by fixing such deformation as it is bycarrying out the hardening heat treatment without correcting thedeformation of the grid member of the grid plate.

The reason for the stepwise press punching lies in the fact thatone-step press punching causes the excessive deformation of the gridmembers. This would result in the degraded quality of the lead gridplate product and, to avoid it, an additional process would be requiredbefore the hardening heat treatment. Such an addition processcomplicates the production work and is not desirable.

The modes of carrying out the multistep press punching process includealternate row punching, alternate line punching and zigzag punching. Incarrying out the press punching process in such modes, it is desirableto avoid the excessive deformation of the grid forming members and toensure the uniform distribution of deformation to a moderate degree.

The deformation of the grid constituent members resulted from themultistep press punching can be left intact and can be fixed as it is bythe hardening heat treatment. However, if so desired, the deformation ofthe grid constituent members may be modified by suitable means beforethe heat treatment.

The sixth object of this invention is to provide a process wherein thedeformation of the grid members caused by the press punching of a rolledlead alloy plate softened by rolling is modified to a suitable sectionalshape before carrying out a hardening process.

Generally, in the lead grid plate obtained by applying a press punchingprocess to a rolled lead alloy plate, the grid forming members of itpresent an angular sectional shape. In the case of an extremely thinplate, such as 0.5 to 1 mm, such a shape presents a problem ofinsufficent active matter retainability.

This problem is solved by this invention. The angular sectional shape ofthe grid constituent members of the lead grid plate press punched, bymeans of a metal mold, from a rolled lead alloy plate is modified bypressing it into a circular or elliptical shape to increase its activematerial retainability to a great degree.

By this process, when the angular sectional shape of the lead alloyplate obtained by press-punching a rolled lead alloy plate is modifiedinto a circular or elliptical shape, the above-stated irregulardeformation is concurrently corrected to such an extent that anotherprocess for correcting or modifying the deformation of the gridconstituent members can be despensed with.

The above-stated modification of the shape of the grid forming memberscan be accomplished by the ordinary pressing process.

The modification of the sectional shape of the grid forming members to acircular or elliptical shape by pressing is accomplished before thehardening heat treatment to obtain a desired product.

In the foregoing, the thickness of the outer frame of the lead gridplate is described to range from 0.5 to 1 mm. However, the presspunching process of this invention is applicable to the manufacture ofother lead grid plates measuring, for example, 1.5 mm in plate thicknessand 0.8 mm in the width of the grid forming members. In such a case,although the thickness of the outer frame is large, the width of thegrid forming members is sufficiently narrow to ensure an increasedactive material retaining ability. Therefore, this invention isapplicable also to lead grid plates having thick outer frames asdescribed below:

The seventh object of this invention is to provide a method formanufacturing lead grid plates wherein the thickness of the outer frameof the lead grid plate is arranged to be in the range from 0.8 to 1.5 mmwhich is thicker than the lead grid plate obtained by the press punchingprocess described in the foregoing; while the thickness of the gridconstituent members inside the frame is arranged to be 0.6 to 0.8 mmwhich is slightly thinner than the grid plate obtained by the abovestated press punching. With the thickness of the inner grid formingmembers thus being arranged to be less than the outer frame, themanufacture of thin lead grid plates can be more easily and steadilycarried out; and yet the active matter retainability can be alsoenhanced thereby.

In the above stated lead grid plate, the inner frame members arearranged to be thinner than the outer frame and to make them stand backfrom the outer frame stepwise in such a manner as to make it activematter retainability much greater than that of the lead grid plate ofeven thickness. The active matter retainability of the lead grid platecan be enhanced to a great extent by such arrangement without anyadditional process for roughening its surface.

Furthermore, since the thickness of the outer frame is increased to bebetween 0.8 and 1.5 mm, the strength of the lead grid plate of the abovestated type is sufficiently great to ensure that it can be manufacturedand handled without fear of deforming it.

Since a relatively thick rolled lead alloy plate measuring between 1.2and 1.5 mm in thickness is employed as a press punching material in thepreparation of the above stated lead grid plate, such a material isobtainable without difficulty and at a low cost. The formation of theinner grid forming members by press punching void parts in therelatively thick rolled lead alloy plate permits carrying out suchpunching in one step without fear of any deformation of the lead gridplate. This also greatly facilitates the manufacture of lead gridplates.

The above-stated lead grid plate is readily obtainable by preparing arolled lead alloy plate of thickness between 0.8 and 1.5 mm; by punchingvoid parts in the plate into a shape of grid; and then by applying apress or the like to the grid forming members in the direction of theirthickness to make them thin.

In the foregoing, the thickness of the outer frame is set between 0.8and 1.5 mm because with the thickness less than 0.8 mm, the lead gridplate is not strong enough to with-stand the press punching andhandling, while, with the thickness exceeding 1.5 mm, the lead gridplate becomes excessively thick. On the other hand, the vertical andtransverse grid members inside the frame is set between 0.6 and 0.8 mmbecause the minimum value of 0.6 mm represents a threashold value inrelation to the problem of galvanic corrosion that takes place inservice, while, with the thickness exceeding 0.8 mm, the difference fromthe thickness of the outer frame becomes insufficient in terms of thequantity of the active material that can be applied and the capabilityof retaining it.

For the actual manufacture of the lead grid plate, there are noparticular limitations as to the width of the outer frame and that ofthe inner frame members. A suitable width of the outer frame can bedetermined in relation to its thickness while that of the inner framemembers can be determined in relation to its final thickness.

It is the eighth object of this invention to provide a method forcontinuously manufacturing lead grid plates with high efficiency and ata low cost, the thickness of their outer frames ranging from 0.8 to 1.5mm with the thickness of their vertical group and transverse group ofgrid forming members or that of at least one of the two groups beingarranged to be thinner than the outer frame and to be within the rangefrom 0.6 to 0.8 mm.

The present invention may be practiced in two different modes, i.e. ModeA and Mode B as described below:

MODE A

A rolled lead alloy plate measuring between 0.8 and 1.5 mm and hardenedby heat treatment is press punched with a metal mold to form gridwindows. Then, at least one of the vertical group or transverse group ofmembers forming the punched grid windows are subjected to a shapemodification process in the direction of thickness of these inner gridmembers to make their thickness between 0.6 and 0.8 mm. After this, theouter frame of the grid is punched out of the lead alloy plate to obtaina lead grid plate usable for batteries. The above-stated hardening byheat treatment may be accomplished by the heat treatment that isconsequently effected immediately after hot rolling or may beaccomplished by a separately arranged heat treatment after cold rolling.

As for the press punching of the grid windows with a metal mold, suchpunching can be accomplished in one step as the rolled lead alloy platehas already been hardened. It is preferable, however, to accomplish suchpunching by a multistep process such as zigzag punching in two steps.

The shape modifying process to be applied to the inner grid formingmembers must be applied to at least one of the vertical or transversegroups of the grid members in the direction of their thickness. In caseswhere such shape modification is applied to one group of the gridmembers, the other group of the grid members are preferably subjected toa process for modifying their sectional shape into a shape differentfrom that of the other group.

As described in the foregoing, the rolled lead alloy plate of thicknessbetween 0.8 and 1.5 mm is subjected to a hardening heat treatmentbecause the lead alloy to be employed in rolling its ingot into a rolledplate of such thickness is a lead-antimony alloy in general. Thehardness of such alloy in the stage of the ingot decreases as the degreeof rolling increases. The decreased hardness of the rolled plate thenmakes the above stated grid window punching process difficult. The heattreatment is carried out to solve this problem.

This hardening heat treatment serves to facilitate the removal ofpunched chips from the mold and makes it possible to easily carry outthe punching without any additional process. With such heat treatmentaccomplished, it is also possible to easily punch inner grid members ofwidth measuring about the same as the plate. By this, the grid membersare free from deformation otherwise caused by press punching, so thatinner grid members of good flatness can be obtained.

When a relatively thick rolled lead alloy plate measuring 0.8 to 1.5 mmis employed as material for punching with the punching first carried outto obtain inner grid windows only, such a rolled lead alloy plate can berather easily obtained at a low cost. Besides, since the press punchingis applied to the relatively thick rolled lead alloy plate to obtain theinner members forming grid windows thereby, a lead grid plate of lessdeformation can be obtained by one-step punching, which, beingcontinuously carried out, greatly facilitates the manufacture of leadgrid plates.

Furthermore, the thickness of the inner grid members is made to be lessthan that of the outer grid frame to make the active material holdingsurface recede either from one side surface or from both side surfacesof the outer frame of the grid plate, so that the active materialretaining quantity per unit area of the lead grid plate can be madegreater than that of a lead grid plate of even thickness. In addition tothat, such increased ability for retaining an active material is furtherincreased with an additional process carried out for roughing thesurface. For this purpose, the inner grid forming members obtained bypunching the grid windows are subjected to a modifying process which iscarried out, for example, by a press or the like in the direction oftheir thickness thus reducing their thickness between 0.6 and 0.8 mm;and in addition to thinning the grid members, the sectional shape of thegrid forming members is modifyed.

In the last place, the lead grid plate is obtained by punching the outerframe with thickness between 0.8 and 1.5 mm. Such lead grid plates canbe continuously manufactured with high efficiency from a lead alloystrip which is produced by a continuous casting machine.

Since the outer frame of the lead grid plate is made thick measuringbetween 0.8 and 1.5 mm, the strength of the unit area of the lead gridplate is also sufficiently great to preclude the fear of deformationduring the manufacture and handling for transportation as well as inservice.

MODE B

A lead alloy plate cold rolled to a thickness of between 0.8 and 1.5 mmis subjected to a press punching with a metal mold to provide gridwindows therein. Following this, a shape modifying process is applied toat least one of the vertical group and the transverse group of the innergrid members forming grid windows after punching. The modifying processis applied in the direction of thickness of these members to reducetheir thickness to within the range from 0.6 to 0.8 mm. Then, the rolledlead alloy plate is hardened by heat treatment before punching the outerframe of the lead grid plate to obtain a lead grid plate for batteries.In this case, the rolled lead alloy plate has been softened through coldrolling. The softened plate facilitates the punching process so that thepress punching by means of a metal mold can be accomplished with a smallpunching force for obtaining the grid windows. This, therefore,minimizes the deformation of the metal mold to ensure a longer servicelife and is advantageous in terms of maintenance.

The hardening heat treatment is carried out before punching the outerframe for the purpose of facilitating the above stated processes ofpunching the grid windows and the shape modification of the inner gridmembers and also for the purpose of imparting a sufficient strength toavoid the deformation that otherwise might take place when an activematerial is applied to the lead grid plate later on.

In Mode A described in the foregoing, when the rolled lead grid platehaving a thickness of between 0.8 and 1.5 mm, and hardened by heattreatment is obtained by subjecting a continuous strip of a lead alloyproduced by a continuous casting process to a hot rolling process tomake its thickness between 0.8 and 1.5 mm, then the continuous massprouction of desired lead grid plates can be accomplished at a low costby continuously carrying out the rolling from the continuous strip, bypunching the grid windows, by shape modifying process on the inner gridmembers and then by punching the outer frame.

In Mode B also, when the cold rolled plate of a lead alloy of thicknessbetween 0.8 and 1.5 mm is to be obtained through a cold rolling processof a continuous strip of a lead alloy produced by a continuous castingprocess, the same advantage can be obtained as in Mode A.

It is the ninth object of this invention to provide a method for thecontinuous mass production at a low cost of lead grid plates forbatteries, wherein an active material fills the grid windows of eachlead grid plate, the outer frame of which measuring between 0.8 and 1.5mm in thickness and at least one of the vertical and the transversegroups of the grid forming inner members is made thinner than the outerframe measuring between 0.6 and 0.8 mm; and wherein the continuous massproduction comprises rolling a continuous strip; punching the gridwindows; shape modification of the inner grid members; applying, fillingand drying of the pastelike active material; and punching the outer gridframe.

In this case, the outer grid frame of thickness between 0.8 and 1.5 mmis punched after the grid windows are filled with the active materialwhich is applied in a paste-like state. The paste of the active materialis dried by an ordinary process after punching the outer frame. Sucharrangement makes it possible to manufacture lead grid plates filledwith an active material for batteries from the continuous strip of alead alloy produced by a continuous casting machine.

The above stated rolled lead alloy plate which measures between 0.8 and1.5 mm and which is hardened by heat treatment is obtained by subjectingthe continuous strip of a lead alloy produced by a continuous castingprocess to a hot rolling process which is carried out to obtain a platethickness of 0.8 to 1.5 mm. In accordance with this method, acontinuous, low-cost mass production of the desired lead grid plate canbe carried out including the rolling of the continuous strip, punchinggrid windows, shape modification of inner grid members, filling themwith the active material, punching the outer frame and drying the activematerial.

The drying of the active material is carried out after punching theouter frame for the following reasons. The active material generallyrequires a long period of time for drying, the material also must bekept enclosed with cloth for a certain period for aging; and it isavantageous to carry out the drying process after separating the unitsof the lead grid plates which have been already filled with the activematerial one after another in terms of process control etc. For dryingthis type of active materials, an ordinary process can be employed.However, it is also possible to carry out such drying in accordance witha heating process essentially comprising heating by means ofelectromagnetic waves. The active material paste prepared throughkneading by a kneading machine is applied to the lead grid plate forbatteries either manually or by mechanical means to fill the voids inthe grid with the paste material, which is then promptly transfered to adrying process. Such drying is generally accomplished by heating in anelectric furnace at a temperature between 60° and 70°C for about 10minutes. The electric furnace is a tunnel furnace in this case measuringabout 10 meters in length. Or, such drying may be accomplished by anelectromagnetic wave heating process for continuous drying. uponcompletion of such drying, each unit is enclosed with cloth and left fora period of about 3 days for aging. Following this, the unit is exposedto air for about 1 day before completion of the drying process.

It is the tenth object of this invention to provide a method whereby themanufacture of the filled plate can be accomplished at a greater speedfor improved efficiency compared with the first method of manufacturingthe filled plate of this invention. Such improved efficiency is attainedby punching the outer frame after the drying of the active material iscompleted following the filling of the grid windows with the material sothat these processes can be carried out in a continuous manner.

Although the heating may be accomplished by an ordinary method inpracticing this method of the invention, the heating process principallycomprising heating with electromagnetic wave is employed for fasterdrying of the filled plates for batteries and for more efficientproduction of such plates. Meanwhile, the conditions of suchelectromagnetic wave heating are controlled to ensure an adequatelydried state to avoid excessive drying which causes cracks, etc. andeventual detachment of the active material in service. In cases of metalproducts, such drying by electromagnetic wave heating causes electricdischarges. Since, in the present invention, the drying object comprisesa kneaded mixture of lead oxide and sulfuric acid which is applied to alead alloy grid, such electric discharge, might takes place whenmoisture content evaporates during the drying process.

In drying the paste of the active material applied to the grid windowsfirst by a heating process principally comprising heating withelectromagnetic waves, therefore, such electric discharges take placewhen the drying continues over an excessively long period of time. Thisdrying process, therefore, should be stopped before arrival of such acritical state.

The active material is virtually dried through the above stated dryingprocess and then is further subjected to another drying process which iscarried out by an ordinary process. However, such additional drying canbe completed within a very short period of time as compared with theconventional process. With the above-stated heating process carried outprincipally by means of electromagnetic waves, the active material isvirtually dried almost instantaneously. By this, therefore, the problemscaused by the conventional heat drying processes such as denaturationduring the drying process is eliminated and, accordingly, suchpreliminary treatment as pickling or steam heating is dispensed with.

The length of time required for the drying of the filled plate by theelectromagnetic wave heating is about 30 seconds which is sufficient forattaining the purpose although it somewhat varies with the compositionof the active material, its moisture content and the distance betweenthe electron tube and the filled plate.

In preparing the paste-like active materials to be used for negativeplates, glycerine may be employed as a kneading liquid while someadditives such as liqnin, reinforcement fiber, water glass, etc. may beadded when necessary.

The other objects, features and advantages of this invention will becomemanifest from the following description and examples.

Furthermore, the heat treatment for hardening is accomplished bycarrying out an aging treatment after an ordinary solution heattreatment. Although the treating conditions are unrestricted, preferredmode of such treatment is carried out by effecting quenching at atemperature between 180° and 230°C and by accomplishing the solutionheat treatment with water at 0°C before aging at room temperature for 24hours.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings,

FIG. 1 illustrates the punching process of this invention.

FIG. 2 illustrates the multistep press punching process of thisinvention; and

FIGS. 3 and 4 are sectional views across lines A-A' and B-B' indicatedin FIG. 2, respectively.

FIG. 5 illustrates an example of the lead grid plate of this inventionprepared for use in batteries.

FIGS. 6, 8 and 10 are sectional views across the line A-A' indicated inFIG. 5.

FIGS. 7, 9 and 11 are sectional views across the line B-B' indicated inFIG. 5.

FIG. 12 illustrates a continuous casting process.

FIG. 13 illustrates the press punching process of this invention.

FIG. 14 is a plan view showing a lead grid plate obtained in accordancewith this invention.

FIG. 15 is a plan view showing a lead grid plate which has beensubjected to a shape modification process.

FIG. 16a and 16b, FIG. 17a and 17b and FIG. 18a and 18b are B-B' andA-A' sectional views of the lead grid plate shown in FIG. 15respectively illustrating it by way of example.

The following description illustrates preferred embodiments of thisinvention.

EXAMPLE 1

In the first process, and ingot of a lead alloy containing 3% Sb and0.3% As and measuring 30 mm in thickness was rolled to 0.8 mm and 0.6 mmin thickness. By this, the hardness of the ingot which was 20 by Vickershardness was decreased to 8.

In the second process, the rolled plate obtained as described above wassubjected to press punching which was accomplished with a metal mold.The metal mold comprises in combination a male mold and a female mold.In this case, it was the female mold that required any attention.

As illustrated in FIG. 1, a zigzag arrangement of void parts 1 waspunched in the first step and then another zigzag arrangement includingthe rest of the void parts 2 is punched in the second step. Another modeof multistep punching was carried out by punching odd rows of voids inthe first step and then even rows in the second step. In addition tothese modes of multistep punching, a singlestep punching process wasalso attempted. By each of these modes of punching, a lead grid platewas obtained with good results of punching. In the drawing, thereference numeral 3 represents transverse grid members; 4 vertical gridmembers; and 5 an outer frame.

The force required for the above stated punching was very small and thefull load was about 300 kg. On the other hand, the punching forcerequired for a base plate that had been hardened by heat treatment was3000 kg at total load.

According to the results of tests for the service life, the metal molddid not show any change after the singlestep punching was repeated 50thousand times.

After the second process, the lead grid plate thus punched was subjectedto a solution heat treatment which was carried out at 230°C for 30minutes and then was subject to natural aging for the purpose ofimproving its mechanical properties. By this, the hardness increased upto a value between 30 and 32 by Vickers hardness which was sufficientfor use as a lead grid plate for batteries.

EXAMPLE 2

An ingot of a lead alloy containing 3% Sb and 0.3% As and measuring 30mm in thickness was subjected to a cold rolling process at a reductionrate of 15% per pass up to 90% to obtain a thickness of 3 mm. The rolledplate was subjected to intermediate annealing at 200°C for 1 hour. Thenthe cold rolling was further carried out to make the thickness about0.95 mm and the plate was again subjected to intermediate annealing at200°C for 1 hour. After this, the final process was carried out by acold rolling with reduction rate of 15% to make the thickness 0.8 mm.The hardened rolled plate of thickness 0.8 mm was subjected to the presspunching process which was carried out as illustrated in the drawing toobtain a lead grid plate with its grid members measuring 0.8 mm inwidth.

The metal mold employed in the punching comprised a male mold which wasprovided with protrusions corresponding to the voids in the lead gridplate and a female mold in which only the parts corresponding to thegrid members of the lead grid plate performed the function of thepunching mold.

EXAMPLE 3

An ingot of a lead alloy which contained 3% Sb and 0.3% As and which was30 mm thickness was rolled to a thickness of 0.8 and 0.6 mm. Thehardness of the ingot was 20 by Vickers hardness. This hardnessdecreased to 8 through the rolling process.

Using a punching metal mold comprising in combination a male mold and afemale mold, the plate was subjected to a punching process which wascarried out by punching a zigzag arrangement of voids 1 in the firststep and then by punching another zigzag arrangement including the restof voids 2 in the second step as illustrated in FIG. 2 through FIG. 4.The width of the parts of the female mold corresponding to the gridmembers of the lead grid plate was set in the range of from 0.5 to 1.0mm which was the same width as that of the grid members of the product.

In addition to the above stated mode of punching, the punching processwas also attempted in a different mode by punching voids in odd rows inthe first step and then by punching voids in even rows in the secondstep. The results obtained by this mode of punching were the same asthose of the above stated mode of punching.

The lead grid plate which was thus prepared with the grid members beingof the same thickness as the plate thickness measuring between 0.5 and 1mm was subjected to a solution heat treatment at 230°C for 30 minuteswith a subsequent natural aging process to obtain a lead grid plate ofVickers hardness 30 to 32.

This lead grid plate permited easy application of an acitve materialthereto with no deformation caused by such work.

EXAMPLE 4

An ingot of a lead alloy (30 mm thick) containing 3% Sb and 0.3% As wasrolled to the thicknesses of 0.8 mm and 0.6 mm.

By the rolling process, the hardness of the ingot which was 20 byVickers hardness is softened to 8.

Then, using a punching metal mold comprising a combination of a malemold and a female mold, a punching process was carried out by punchingvoids in a zigzag arrangement in the first step and the rest of thevoids were punched also in a zigzag manner in the second step asdescribed in Example 3. The width of the parts of the female moldcorresponding to the grid members of the lead grid plate was set between0.5 and 1.0 mm in the same manner as the members of the grid product.

There was a slight degree of deformation resulting from the uniformpress punching in each member of the lead grid plate which was obtainedby the above-stated two-step zigzag press punching.

The lead grid plate in which the width of the grid members was equal tothe thickness of the plate, both measuring between 0.5 and 1 mm wassubjected to a solution heat treatment at 230°C for 30 minutes, followedby a natural aging treatment. By this, a lead grid plate of Vickershardness between 30 and 32 was obtained.

The deformation of the grid members of the lead grid plate served toincrease the adhering quantity of the active material and also toeffectively prevent the active material from detaching.

EXAMPLE 5

An ingot of a lead alloy containing 3% Sb and 0.3% As and measuring 30mm in thickness was rolled to thicknesses of 0.8 and 0.6 mm.

The hardness of the ingot which was 20 by Vickers hardness was softenedto a value of 8 through this rolling process.

Following this, voids were punched using a punching metal moldcomprising a combination of a male mold and a female mold in such amanner as described in Example 3. For this punching the width of theparts of the female mold corresponding to the width of the grid membersof the product was set between 0.5 and 1.0 mm which was equal to thewidth of the grid members of the product.

After the above-stated press punching, the grid members were subjectedto pressing which is carried out in an ordinary process for modifyingthe sectional shape of the grid members to a circular shape.

The lead grid plate was then subjected to a solution heat treatment at230°C for 30 minutes followed by a natural aging to make its hardnessbetween 30 and 32 by Vickers hardness.

With the grid members modified to a circular sectional shape, the leadgrid plate thus obtained was capable of retaining an active material inquantity about 10% more than the quantity retainable by the grid membersof a square sectional shape.

EXAMPLE 6

A rolled plate of a lead alloy containing 3% Sb and 0.3% As andmeasuring 1.5 mm in thickness was subjected to a single-step presspunching process to punch voids 21 as shown in FIG. 5. By this, a baseplate of a lead grid comprising 13 transverse members and 2 verticalmembers was obtained. In this stage, all of the outer frame 22, theinner transverse members 23 and the inner vertical members 24 measured1.5 mm in thickness with the width of the outer frame 22 measuring 2.0mm.

Then, a shape modifying process was applied to the transverse members 23and the vertical members 24 by means of a press. By this, the verticalmember 24 was changed into a regular hexagonal shape, each sidemeasuring 0.31 mm, as shown in FIG. 6. Thus, both the width and thethickness of each vertical member 24 were made to measure 0.78 mm andthe face of each vertical member 24 was made to recede (1.5 - 0.78) ÷ 2= 0.36 mm from the faces 25 and 25' of the outer frame 22.

On the other hand, the transverse members 23 were processed to changetheir sectional shape into a semi-trapezoid shape with both bottom sideschamfered as shown in FIG. 7. Referring to FIG. 7, the upper side ofevery other transverse member 23 was positioned on the same plane as theface 25 of the outer frame while the upper sides of the rest of thetransverse member 23 was on the same plane as the other face 25' of theouter frame, the lower sides of all transverse members thus recedingfrom the surface 25 or surface 25' of the outer frame.

The upper side of the above-stated trapezoid measures 0.7 mm, itschamfered bottom 2.3 mm and its height 0.7 mm. Therefore, the face ofeach transverse member receded from the surface 25 or 25' of the outerframe by 1.5 - 0.7 = 0.8 mm.

In this manner a lead grid plate in which all of the transverse andvertical members were receding from the faces of the outer frame wasobtained for use in a battery applicable to motorcycles.

EXAMPLE 7

A lead grid plate for batteries was prepared in a similar manner as inExample 6. As shown in FIG. 7, the outer frame 22 measures 20 mm inwidth and 0.8 mm in thickness. Each vertical grid member 24 which wasshaped into a flat hexagonal sectional shape measures 0.6 mm inthickness and 1.7 mm in width with its horizontal face measuring 0.5 mmin length. Each transverse member which was of semi-trapezoid sectionalshape with both bottom sides chamfered measures 0.5 mm in width on theupper side, 1.34 mm in width on the bottom side and 0.6 mm in thickness.

Accordingly each of the vertical grid members 24 receded about 0.1 mmfrom the face 25 or 25' of the outer frame 22 while each of thetransverse members 23 receded 0.2 mm from the face 25 or 25' of theouter frame.

EXAMPLE 8

A lead grid plate for batteries applicable to motorcycles was preparedas shown in FIG. 7 and FIG. 8 in a similar manner as described inExample 6. The details of the product are as shown below:

    Outer frame Thickness:                                                                              1.2 mm                                                              Width:    2.0 mm                                                  Vertical member                                                                           Shape:    Sidewise, flat hexagonal                                            Thickness:                                                                              0.8 mm                                                              Width:    1.6 mm (of which horizontal                                                   face length is 0.8 mm)                                  Transverse member                                                                         Shape:    Semi-trapezoid with both                                                      bottom side chamfered                                               Thickness:                                                                              0.5 + 0.2 (chamfered part)                                                    = 0.7 mm                                                            Width:    1.8 mm                                                   Vertical member receding distance from outer frame:                             (1.2 - 0.8) ÷ 2 = 0.2 mm                                                Transverse member receding distance from outer frame:                           1.2 - 0.7 = 0.5 mm                                                     

EXAMPLE 9 1. Rolling Process

In the case of cold rolling, rolling was carried out in the followingsequence without intermediate annealing:

                         →1.3 mm → 0.8 mm                           5.0 mm→4.0 mm→3.0 mm→2 mm                                                     →1.2 mm                                                                →1.5 mm                                       

For hot rolling, rolling was carried out at a heating temperaturebetween 190° and 210°C in a stepwise manner as shown below:

                         →1.5 mm                                           5 mm→2.5 mm   →1.2 mm                                                                →1.2 mm→0.8 mm                         

In the case of the hot rolling process, a hardening heat treatment wasaccomplished by carrying out a solution heat treatment process with orwithout water cooling immediately after the hot rolling.

2. Hardening Process by Heat Treatment

Since a hardening treatment was effected in the process of hot rollingas mentioned in the foregoing, a hardening treatment was carried outonly when cold rolling was accomplished. By using a tunnel furnace, acold rolled plate was heated at a temperature between 210° and 220°C for30 minutes and was cooled with water to harden it.

3. Press Punching

As shown in FIG. 13, holes 111 were first provided for the purpose ofdetermining positions in both sides of a continuous strip of a rolledlead alloy plate 110 which had been hardened by heat treatment. Afterthis, grid windows 12 were punched.

In a preferred mode of the punching process, one zigzag arrangement ofgrid windows 112-1 were punched in the first step of punching and thenthe other zigzag arrangement of grid windows 112-2. In this manner,plates of thickness 1.5 mm, 1.2 mm and 0.8 mm were punched. However, thewidth of the transverse and vertical grid members was set at 0.8 mm inall cases of these different plate thicknesses. The punching frequencyof the press was set at 60 times/minute.

4. Shape Modification

Without any additional process, the press punched transverse andvertical members of the grid measures 0.8 mm in width and 1.5 mm, 1.2 mmor 0.8 mm in thickness. Therefore, in the case of the transverse members13 as shown in FIG. 14, a shape modification was accomplished to make itinto a sectional shape of an upside-down trapezoid measuring 2.3 mm, 1.8mm or 1.34 mm in bottom length and 0.7 mm, 0.7 mm or 0.6 mm in height.As for the vertical grid members 14, modification was made, forinstance, into a regular hexagon sectional shape. The active materialretainability was increased by such shape modifying processes.

The shape modification was carried out by means of a press with a metalmold which consisted of upper and lower halves. The shape modifyingprocess frequency was 60 times/minute.

Referring to FIG. 15 through FIG. 18, the details of this shapemodifying process will be understood from the following description:

Shape Modification Example 1

FIGS. 16a and 16b and FIG. 15 are B-B' and A-A' sectional views showingthe sectional shapes of transverse and vertical grid members which haveundergone the shape modifying process. The transverse members 113 arearranged in such a manner that every other member recedes from one sideface of the outer frame 115 while each of other alternating membersrecede from the opposite side face of the outer frame 115. The sectionalshape of the transverse members presents a trapezoid shape the upperside of which faces the outward direction and the lower side faces theinward direction, both edges of the lower side being chamfered. On theother hand, the vertical members 114 are arranged to recede from theboth side faces of the outer frame 115 with their sectional shapepresenting a semiregular hexagonal shape disposed sidewise.

Shape Modification Example 2

As shown in FIG. 17a and 17b, the transverse grid members 113 aredisposed to recede from both side faces of the outer frame 115 with thetransverse members being of a rectangular sectional shape. The verticalgrid members 114 are arranged in the same manner as in the ShapeModification Example 1.

Shape Modification Example 3

As shown in FIGS. 18a and 18b, every other transverse grid member 113 isdisposed to recede from only one side face of the outer frame 115 while,alternately, the rest of the transverse members 113 are disposed torecede from only the opposite side face of the outer frame 115, thetransverse members 113 being of a rectangular sectional shape. The shapeof vertical members 114 is not modified in this example.

5. Outer Frame Punching Process

The rolled lead alloy plate 110 which had been processed with gridwindows 112 punched and the inner grid members modified in shape wassubjected to the outer frame punching process to obtain a lead gridplate product as illustrated in FIG. 14. The grid plate was usable as aplate for a battery applicable to motorcycles, the grid comprising 13transverse members 113 and 2 vertical members 114.

EXAMPLE 10 1. Rolling Process

Without intermediate annealing, a rolling process was carried out in thefollowing sequence:

                        1.3 mm 0.8 mm                                             5.0 mm 4.0 mm 3.0 mm 2 mm                                                                         1.2 mm                                                                        1.5 mm                                                

2. Press Punching Process

Carried out in the same manner as in Example 1.

3. Shape Modifying Process

Carried out in the same manner as in Example 1.

4. Hardening by Heat Treatment

The rolled lead alloy plate which was processed by punching grid windowsand by shape modifying grid members was continuously passed through afunnel furnace for heating at 210° to 220°C for 30 minutes and thenhardened by water cooling, then carried out for hardening.

5. Outer Frame Punching Process

Carried out in the same manner as in Example 1.

EXAMPLE 11

FIG. 12 illustrates a continuous casting device which comprises aninternal cooling type casting wheel 101 measuring 1.5 meters in diameterand an endless steel strip 102 of 2 mm thickness which is in contactwith the periphery of the casting wheel to move as the wheel 101 isdriven by a motor. A casting mold is formed between a groove provided inthe circumference of the wheel 101 and the steel strip 102, which isguided by guide rolls 103.

The molten lead alloy was poured into the casting mold through a moltenmetal casting port 104 disposed in the upper part of the device at acontact starting point between the casting wheel 101 and the strip 102,the molten alloy was cooled as the wheel 101 and the strip 102 rotate inthe direction of arrow and a lead alloy strip 105 was continuouslyobtained from the lower part of the casting device. The composition andthe casting conditions of the lead alloy are as shown in the followingtable.

    Example 1    Example 2  Example 3                                             ______________________________________                                        Sb, % 2          3          4                                                 As, % 0.2        0.3        0.4                                               Pb, the remainder                                                             Casting temperature: 350 to 400°C                                      Casting wheel rotating speed:                                                   3 meters/min. to 7 meters/min.                                              Dimensions of the mold part in the molding wheel:                               5 mm in thickness and 140 mm in width                                       ______________________________________                                    

Lead grid plates were obtained from the strips thus obtained throughprocesses carried out in accordance with Example 9 or 10 as desired.

EXAMPLE 12

The continuous casting process, rolling process, hardening by heattreatment, press punching process and shape modifying process werecarried out in accordance with Example 11. Following these processes,the lead grid plate was filled with an active material by a process asshown below:

6. Active Material Filling Process (for positive plate)

The above-stated grid windows were filled with an active material byapplying it to the lead grid plate by means of a pallet, the activematerial consisting of 40% by weight of PbO and 60% by weight of PbOwith 1 liter of water and 1.4 liters of sulfuric acid (specific gravity:1.3200) added to obtain total 10 kg of paste of the material.

7. Outer Frame Punching Process

An undried filled plate as shown in FIG. 3 was obtained by punching theouter frame of the lead grid plate from a rolled lead alloy plate 10which had been processed by punching grid windows 12 and shape modifyinginner grid members.

8. Drying Process

The above stated undried filled plate was continuously passed through atunnel furnace measuring 10 meters in length for heating at 60° to 70°Cfor about 10 minutes. The heated plate was wrapped in cloth for agingfor 3 days and then exposed to air for 1 day to obtain a dried filledplate. The filled plate thus obtained was usable as a plate for abattery applicable to motorcycles. The plate consisted of 13 transversemembers 13 and 2 vertical members 14.

EXAMPLE 13 1. Continuous Casting Process

Carried out in the same manner as in Example 12.

2. Rolling Process

The rolling process was carried out in the following sequence withoutcarrying out intermediate annealing:

    5.0 mm→4.0 mm→3.0 mm→2 mm                                                    →1.3 mm→0.8 mm                                                  →1.2 mm                                                                →1.5 mm                                        

3. Press Punching Process

Carried out in the same manner as in Example 1.

4. Shape Modification:

Carried out in the same manner as in Example 1.

5. Hardening by Heat Treatment

A rolled lead alloy plate which had been processed by punching gridwindows and by shape modifying grid members was continuously passedthrough a tunnel furnace for heating at a temperature of between 210°and 220°C for 30 minutes and then hardened by water cooling.

6. Active Material Filling Process

Carried out in the same manner as in Example 1.

7. Outer Frame Punching Process

Carried out in the same manner as in Example 1.

8. Drying Process

Carried out in the same manner as in Example 1.

EXAMPLE 14

The following process was carried out after completion of (1) continuouscasting process through (6) active material filling process of Example12.

7. Drying Process

Using an electronic oven (output 450 W), drying was carried out to astate before the state in which there would take place electricdischarges. The distance between the electron tube and the lead gridplate was 250 mm. The results of the drying process are as shown below:

    Heating time      Drying degree                                               ______________________________________                                        10 seconds                                                                             Insufficient drying. Active material comes off                       15 seconds                                                                             Insufficient drying. Active material comes off                       20 seconds                                                                             Insufficient drying. Active material comes off                       30 seconds                                                                             Sufficiently dried. No cracks, no coming                                      off of material.                                                     40 seconds                                                                             Excessively dried. Electric discharge takes                                   place causing partial detachment of active                                    material.                                                            ______________________________________                                    

By carrying out this example, it was found that the period of time forcarrying out heating by means of electromagnetic waves should be from 20± 40 seconds and preferably about 30 seconds. It was thus confirmed thatcompared with the conventional heating process which requires heatingfor 10 minutes covering 10 meters of the plate, the drying time isshortened to a great degree.

Following the above, the filled plate dried by the ordinaryelectromagnetic wave heating process was wrapped in cloth for furtherdrying for 3 days and then exposed to air for 1 day to complete drying.During this period, the PbO contained in the active material wassomewhat modified by the sulfuric acid contained in the active material.As a result of this, the active material applied no longer got off.

8. Outer Frame Punching Process

Carried out in the same manner as in Example 1 to obtain a filled plate.

EXAMPLE 15

In accordance with Example 13, (1) continuous casting process through(5) hardening by heat treatment process were carried out. After this,the following processes were carried out.

6. Filling and Drying of Active Material (for negative plate)

The active material component consisting of 20% by weight of Pb and 80%by weight of PbO was blended with 0.6 liter of water and 1 liter ofsulfuric acid (specific gravity: 1.320) to obtain 10 kg of a paste-likeactive material. After applying this material by means of a pallet,drying was carried out with an electronic oven (output 450 W) to obtainresults as shown below.

    Heating time      Drying degree                                               ______________________________________                                        10 seconds                                                                             Insufficiently dried. Active material                                         comes off.                                                           20 seconds                                                                             Sufficiently dried                                                   25 seconds                                                                             Sufficiently dried                                                   30 seconds                                                                             Sufficiently dried                                                   40 seconds                                                                             Excessively dried. Electric discharge                                         takes place causing partial detachment                                        of active material.                                                  ______________________________________                                    

The above table indicates that, in accordance with this example, thetime for heating should be from 10 to 40 seconds and preferably from 20to 30 seconds.

The subsequent process for drying is carried out by an ordinary processin the same manner as in Example 14 to obtain a dried product.

7. Outer Frame Punching Process

Carried out in the same manner as in Example 3 to complete a filledplate.

What is claimed is:
 1. A method for manufacturing a lead grid platehaving an outer frame portion for batteries comprising the first step ofpreparing a rolled lead alloy plate measuring 0.5 to 1 mm in thickness;and the second step of press punching the rolled lead alloy plate bymeans of a metal mold to obtain a lead grid plate, the width of the gridforming members of the plate measuring about the same as the thicknessof the plate, said second step being accomplished in at least two stepsby press punching only voids at least in every alternate file or row orin a zig-zag line, then filling the lead grid plate with activematerial.
 2. A method for manufacturing a lead grid plate having anouter frame portion for batteries according to claim 1, which furthercomprises the step of hardening the lead grid plate by a heat treatment.